Snapshot system

ABSTRACT

A storage system including: a disk device including an original volume and a plurality of snapshot generations; and a storage control unit which includes a processor unit. The processor unit receives write data to a storage area of the original volume, and determines whether data stored in the storage area of the original volume is already copied to the snapshot volume or not; if the data stored in the storage area of original volume is not already copied to snapshot volume, the processor unit copies the data from original volume to the snapshot volume, when a use capacity of the snapshot volume is larger than threshold amount by the copy, the processor unit indicates a specified snapshot generation, the processor unit migrates data of the specified snapshot generation from the snapshot volume to tape device; the processor unit deletes information of the specified snapshot generation in the snapshot volume.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 12/054,846, filedMar. 25, 2008 now U.S. Pat. No. 7,606,990, which is a continuation ofU.S. application Ser. No. 10/998,755, filed Nov. 30, 2004 (now U.S. Pat.No. 7,356,658). This application relates to and claims priority fromJapanese Patent Application No. 2004-293464, filed on Oct. 6, 2004. Theentirety of the contents and subject matter of all of the above isincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a storage system for obtaining a snapshot of avolume image in a computer system which uses a storage, and moreparticularly to obtaining of an image of an optional generation volume.

In an information-oriented society, one of the important roles of thestorage system that stores information is data protection. A most commonmethod of data protection is so-called backup which stores data of thestorage in a backup medium such as a tape library. In the backup, evenif data of the operated storage system is lost due to a failure,interference, an operation mistake, or the like, the data of the storedtime can be recovered by restoring backup data, whereby damage can belimited to a minimum.

However, a larger capacity of the storage is accompanied by an increasein time necessary for backup. Additionally, in use of high data updatingfrequency, a difference from the backup data is shortly increased evenwhen the data is backed up once. Thus, backup data must be frequentlygenerated in case that damage will increase. To deal with a file losscaused by an operation mistake or the like, or to prepare for comparisonof file contents with a past state, there is a wish to easily refer todata which is periodically backed up.

A snapshot has been a focus of attention as a function to meet such use.The snapshot stores an image of data of the storage operated at thetime. The snapshot image can be accessed as a volume different from thatof the operated storage.

As the snapshot function, there has been presented a generationmanagement method of a snapshot image in which a data holding unit 1executes normal reading, a data holding unit 2 stores a snapshot imageof the data holding unit 1 at a given time, a data holding unit 3 storeshistory information containing update data which accompanies datarewriting in the data holding unit 1 after the time of storing thesnapshot image in the data holding unit 2, information indicating ageneration thereof, and information indicating an update area thereof,and a data reading source selection unit refers to each historyinformation stored in the data holding unit 3 to obtain a store locationof a snapshot image to be read according to designation of a generationand an area of the snapshot image to be read, and switches data readingsource to one of the data holding unit 2 and the data holding unit 3according to the store location (e.g., JP 2002-278819 A).

SUMMARY OF THE INVENTION

The snapshot function stores snapshot information only of an originalvolume. Thus, many snapshots must be stored to store many generations,consequently increasing a storage capacity.

On the other hand, backup data of many generations can be stored in thetape library. However, the tape library is only suited to storage ofdata of low access frequency because an access speed is generally veryslow. Thus, the tape library is not suited to requested high-speedaccessing or restoring of data of many generations. Backup data ispreferably stored in a storage control unit.

This invention has been made with the foregoing problems in mind, and itis an object of this invention to provide a storage system which canstore backup data of many generations in a storage of a storage controlunit, and access and restore the data.

According to an embodiment of this invention, there is provided astorage system including: a disk device which includes: an originalvolume from/to which data is read/written by a host; a copy volume forstoring a copy of the original volume of a predetermined timing; and asnapshot volume for storing snapshot data of a snapshot of the originalvolume; and a storage control unit which includes: a management unit forcontrolling the storage control unit; a channel I/F that is connected tothe host; and a device I/F that is connected to the disk device, whereinthe management unit copies data of the original volume to the copyvolume by a predetermined timing, stores the snapshot data of thesnapshot in the snapshot volume corresponding to a write request in theoriginal volume, manages a generation of the created snapshot and ageneration of the copy volume, and reads data from at least one of thesnapshot volume and the copy volume when a read request from a volume ofa generation different from that of the original volume is received fromthe host.

According to an embodiment of this invention, it is possible to obtainoptional volumes of a plurality of generations by storing the snapshotvolume and the copy volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a storage systemaccording to a first embodiment of this invention.

FIG. 2A is an explanatory diagram showing a snapshot management table ofa snapshot bitmap according to the first embodiment of this invention.

FIG. 2B is an explanatory diagram showing a snapshot block managementtable of the snapshot bitmap according to the first embodiment of thisinvention.

FIG. 3 is a flowchart of a writing process according to the firstembodiment of this invention.

FIG. 4 is a flowchart of a reading process according to the firstembodiment of this invention.

FIG. 5 is a flowchart of a snapshot creation process according to thefirst embodiment of this invention.

FIG. 6 is a flowchart of a copy volume creation process according to thefirst embodiment of this invention.

FIG. 7 is a flowchart of a designated generation volume creation processaccording to the first embodiment of this invention.

FIG. 8 is a flowchart of a process of accessing a designated generationvirtual volume according to the first embodiment of this invention.

FIG. 9 is a flowchart of an original volume restoration processaccording to the first embodiment of this invention.

FIG. 10 is a flowchart of a designated generation volume creationprocess according to the first embodiment of this invention.

FIG. 11 is a flowchart of a snapshot volume capacity management processaccording to the first embodiment of this invention.

FIG. 12 is a flowchart of a process of restoring data of an originalvolume according to the first embodiment of this invention.

FIG. 13 is a flowchart of a process of restoring data of an originalvolume according to the first embodiment of this invention.

FIG. 14 is a flowchart of a copy volume creation process according to asecond embodiment of this invention.

FIG. 15 is a flowchart of a designated generation volume creationprocess according to the second embodiment of this invention.

FIG. 16 is a flowchart of a designated generation volume creationprocess according to the second embodiment of this invention.

FIG. 17 is a flowchart of a designated generation volume creationprocess according to the second embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of this invention will be describedwith reference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a storage system.

A storage control unit 200 provides file share services to a host 100connected through a channel interface (channel I/F) 210.

The storage control unit 200 includes a channel I/F 210, a CPU 220, adevice interface (device I/F) 230, and a memory 240.

The channel I/F 210 is connected to the host 100 through a network totransmit/receive a predetermined signal (command, data).

The device I/F 230 transmits/receives a signal (command, data) based onSmall Computer System Interface (SCSI) with a storage 300.

The storage 300 includes a plurality of disk devices, which are dividedinto three logical areas (logical volumes), i.e., an original volume310, a copy volume 320, and a snapshot volume 330.

The original volume 310 is a logical volume from/in which data isread/written based on a request from the host 100. The copy volume 320functions as a backup to store a full copy of the original volume 310 ofa given time. The snapshot volume 330 stores a snapshot of the originalvolume 310.

The memory 240 stores a snapshot management program 241, a generationvolume create program 242, an original volume restore program 243, and asnapshot volume capacity management program 244. The CPU 220 loads andexecutes these programs to managing the storage unit.

The memory 240 includes a cache memory 250 and a common memory 260. Thecache memory 250 functions as a cache when data is written/read in/fromthe storage 300. The common memory 260 stores control information or thelike used for various operations of the storage control unit 200. Thecommon memory 260 stores a snapshot bitmap 261, a copy volume generationmanagement information 262, snapshot information 263, volume capacitymanagement information 264, and the like.

The snapshot bitmap 261 includes a snapshot management table 2610 and asnapshot block management table 2620 (described later). The copy volumegeneration management information 262 registers information regardingwhich generation data copied in the copy volume 320 belong to. Thesnapshot information 263 registers information regarding a time ofstoring a snapshot in the snapshot volume 330 and a generation thereof.The volume capacity management information 264 registers informationregarding a use capacity of a snapshot volume of each generation, a lastaccess date and time, and access frequency.

Upon reception of a snapshot creation request from the host 100, thesnapshot management program 241 creates a snapshot of the originalvolume 310 of the storage control unit 200. In the snapshot creationprocess, by using the snapshot management table 2610 (described later),the snapshot management program 241 manages data stored in the originalvolume 310 and the snapshot volume 330 to enable access to the datastored in the original volume 310 at the time of receiving the snapshotcreation request. Accordingly, access can be made to a virtual volumefor providing the created snapshot of the original volume 310.

The virtual volume includes storage areas in one or a plurality of diskdevices. In reality, the virtual volume includes a block in the originalvolume 310 and a block in the snapshot volume 330.

The snapshot management program 241 manages a volume (snapshot volume330) which stores snapshot data necessary for maintaining the snapshotin addition to a volume (original volume 310) which stores a filesystem, and executes a data input/output process, a process ofmaintaining the snapshot or a process of making the snapshot usableaccording to a request from the host 100.

Specifically, the snapshot management program 241 receives the snapshotcreation request. The snapshot management program 241 that has receivedthe creation request first registers identification information of a newvirtual volume in the snapshot management table 2610 (described later).A block of the virtual volume is correlated one by one to a block of theoriginal volume 310 initially based on the snapshot management table2610. However, when data in the original volume 310 is updatedthereafter, the snapshot management program 241 copies the data beforeupdating from the original volume 310 to the snapshot volume asdescribed later, and updates stored data of the original volume 310after the copying. Then, the snapshot management program 241 updates thesnapshot management table 2610 to correlate the block of the virtualvolume corresponding to the data-updated block of the original volume310 to a block of the snapshot volume which has stored the data storedin the original volume 310 at the time of receiving the snapshotcreation request (i.e., data before updating).

The snapshot management program 241 receives an access request thevirtual volume from the host 100. The snapshot management program 241that has received the access request refers to the snapshot managementtable 2610 to instruct the host 100 to access the block of the originalvolume 310 or the block of the snapshot volume 330 correlated to theblock of the virtual volume. Accordingly, the host 100 can obtaininformation of the original volume 310 at the time of the snapshotcreation request by accessing the virtual volume. Thus, the storagecontrol unit 200 can provide a snapshot image of the file system.

The operations will be described in detail later.

The storage 300 may use a plurality of independent physical disk drives,or physically divide one disk drive by logical division. Alternatively,the storage 300 may be a logical volume which includes a plurality ofdisk devices and which is logically set as one disk. Otherwise, a RAIDdevice may include a plurality of physical disk drives which constitutea logical volume.

The tape library 400 stores the copy of the data stored in the storage300 connected to the storage control unit 200. The tape library 400 isconnected through the channel I/F 210 to the storage control unit 200.

The host 100 includes a program 110. The storage control unit 200includes an I/F 270. The I/F 270 is connected to a terminal 500 througha LAN 501. For example, the I/F 270 includes an SCSI interface.

A user can send instructions to the storage control unit 200 by theprogram 110 of the host 100.

The user can also send instructions to the storage control unit 200 fromthe terminal 500.

FIGS. 2A and 2B are explanatory diagrams of the snapshot bitmap 261.

The snapshot bitmap 261 includes the snapshot management table 2610shown in FIG. 2A and the snapshot block management table 2620 shown inFIG. 2B.

The snapshot management table 2610 shown in FIG. 2A includes an originalvolume block address 2611, a generation management bitmap 2612, and avirtual volume generation access table.

A column 2611 registers block addresses of the original volume 310. A1st block address No. 0 of the original volume 310 is allocated to afirst line (1st line), a block address No. 1 of the original volume isallocated to a 2nd line, block addresses of the original volume 310 areallocated sequentially thereafter, and a block address No. (m-1) of theoriginal volume 310 is allocated to an m-th line which is a last line.

A column 2612 is a generation management bitmap, which indicates whetherthere is snapshot data or not corresponding to the original volume blockaddress. Details will be described later.

Columns 2613 to 2615 register data store locations corresponding toblock addresses of virtual volumes of generations. For example, thecolumn 2613 registers a data store location of a snapshot No. 1(generation 1). In this case, the snapshot number and the virtual volumenumber are identical, and the number indicates a generation. Forexample, a virtual volume 1 corresponds to a snapshot No. 1, and ageneration of the virtual volume 1 is “1”.

A 1st line of the column 2613 registers information for identifying astorage area in which data corresponding to a block address No. 0 of thevirtual volume 1 of the generation 1 is stored. Sequentially thereafter,a 2nd line registers a data store location corresponding to a blockaddress No. 1 of the virtual volume 1, a 3rd line registers a data storelocation corresponding to a block address No. 2, and the like.

More specifically, No. 0 registered as the data store location of theblock address No. 0 of the virtual volume 1 in the 1st line correspondsto a block address No. 0 of the snapshot volume 330.

The snapshot management program 241 receives a snapshot creationrequest. When data of the block address No. 0 of the original volume 310is updated, the snapshot management program 241 that has received thecreation request writes data before updating stored in the block addressNo. 0 of the original volume 310 in the block address No. 0 of thesnapshot volume 330. Subsequently, the data of the block address No. 0of the original volume 310 is updated. It is because the data stored inthe original volume 310 at the time of receiving the snapshot creationrequest must be stored in one of the storage areas in the disk device toprovide access to the snapshot.

As described above, in the snapshot management table 2610, the blockaddress No. 0 of the virtual volume 1 is correlated to the block addressNo. 0 of the snapshot volume 330. The snapshot management program 241can obtain the data before updating of the block address No. 0 of theoriginal volume 310, i.e., the virtual volume of the generation 1, byaccessing the 1st-line block address No. 0 of the virtual volume 1,i.e., the block address No. 0 of the snapshot volume 330.

Accordingly, upon reception of an access request the block address No. 0of the virtual volume 1 of the generation 1, the snapshot managementprogram 241 refers to the snapshot management table 2610 to access theblock address No. 0 of the snapshot volume 330. As a result, thesnapshot management program 241 can provide, to the host 100, anenvironment of access to the virtual volume 1 of the generation 1 in astate similar to that in which the data before updating of the blockaddress No. 0 of the original volume 310, i.e., the data of thegeneration 1 stored in the block address No. 0 of the original volume310 at the time of receiving the snapshot creation request, has beenwritten in the block address No. 0 of the virtual volume 1.

Similarly, No. 1 registered as a data store location of the blockaddress of the virtual volume 1 of the generation 1 in the 2nd linecorresponds to a block address No. 1 of the snapshot volume 330. Whendata of the block address No. 1 of the original volume 310 is updatedafter the reception of the snapshot creation request, the snapshotmanagement program 241 writes data before updating of the block addressNo. 1 of the original volume 310 in the block address No. 1 of thesnapshot volume 330. Subsequently, the data of the block address No. 1of the original volume 310 is updated. Thus, in the snapshot managementtable 2610, the block address No. 1 of the virtual volume 1 of thegeneration 1 is correlated to the block address No. 1 of the snapshotvolume 330. The snapshot management program 241 can provide, to the host100, access to the virtual volume 1 of the generation 1 in a statesimilar to that in which the data before updating of the block addressNo. 1 of the original volume 330, i.e., the data of the generation 1,has been written in the block address No. 1 of the virtual volume 1.

In the 3rd to the m-th line, “NONE” is registered as store locationinformation corresponding to data of the block addresses No. 2 to No.(m-1)-th of the virtual volume 1. The “NONE” indicates a block addresscorresponding to the original volume 310. Thus, block addresses No. 2 toNo. (m-1)-th of the original volume 310 correspond to the blockaddresses No. 2 to No. (m-1)-th of the virtual volume 1. In other words,the “NONE” indicates that a relevant block of the original volume 310has not been updated (rewritten) after the last reception of thesnapshot creation request.

As a result, the snapshot management program 241 can provide a snapshotimage of the original volume 310 at a time before the updating of thedata of the block addressees Nos. 0 and 1 of the original volume 310,i.e., the virtual volume 1 of the generation 1, based on the data of theblock address No. 0 of the virtual volume 1, the data of the blockaddress No. 1 of the virtual volume 1, and the data of the blockaddresses No. 2 to No. (m-1)-th of the original volume 310.

The column 2614 registers a data store location of a virtual volume 2 ofa generation 2.

Each time the snapshot management program 241 receives the snapshotcreation request, the snapshot management program 241 registers avirtual volume of a new generation in the snapshot management table toobtain a snapshot at the time of receiving the creation request. Thevirtual volume 2 is of a generation corresponding to a snapshot of asnapshot No. 2 (generation 2) created by the snapshot management program241 when a snapshot creation request (snapshot creation request ofgeneration 2) is received again after the creation of the snapshot ofthe snapshot No. 1 (corresponding to the virtual volume 1 of thegeneration 1).

No. 0 registered as the data store location of the block address No. 0of the virtual volume 2 in the 1st line of the column 2614 correspondsto a block address No. 0 of the snapshot volume 330.

The snapshot management program 241 receives a second snapshot creationrequest. When data of the block address No. 0 of the original volume 310is updated, the snapshot management program 241 that has received thecreation request copies the data before updating stored in the blockaddress No. 0 of the original volume 310 in the block address No. 0 ofthe snapshot volume 330 as described above. Subsequently, the data ofthe block address No. 0 of the original volume 310 is updated. Then, thesnapshot management program 241 rewrites the snapshot management table2610 to store data corresponding to the block addresses Nos. 0 of thevirtual volume 1 and the virtual volume 2 in the block address No. 0 ofthe snapshot volume 330, and to correlate the block addresses Nos. 0 ofthe virtual volume 1 and the virtual volume 2 to the block address No. 0of the snapshot volume 330.

No. 2 registered as a data store location of the block address No. 1 ofthe virtual volume 2 in the 2nd line of the column 2614 corresponds to ablock address No. 2 of the snapshot volume 330. It indicates that afterthe snapshot management program 241 receives the second snapshotcreation request, the data of the block address No. 1 of the originalvolume 310 is updated. In other words, for the data updating of theblock address No. 1 of the original volume 310 after the reception ofthe second (generation 2) snapshot, the data before updating has beencopied to the block address No. 2 of the snapshot volume 330. It isbecause copying to the block address No. 1 of the snapshot volume 330causes a change in the data correlated to the block address No. 1 of thevirtual volume 1, destroying the first snapshot data.

In the 3rd to the m-th line of the column 2614, “NONE” is registered asstore location information of data of the block addresses No. 2 to No.(m-1)-th of the virtual volume 2. As described above, the “NONE”indicates that the block address of the virtual volume is correlated toa corresponding nonupdated block address of the original volume 310.

The virtual volume n is similar to the virtual volumes 1 and 2, and thusdescription thereof will be omitted.

The column 2612 is a generation management bitmap. A bit number thereofis equal to the number of virtual volumes. In the case of FIG. 2A, ageneration management bitmap has n bits as the number of virtual volumesis n. A 1st bit of the generation management bitmap corresponds to thevirtual volume 1 of the generation 1, a 2nd bit corresponds to thevirtual volume 2 of the generation 2, and similarly thereafter an n-thbit corresponds to the virtual volume n of the generation n. When thereis updating registration in a k-th line block address of the virtualvolume, i.e., when the block address of the snapshot volume 330 has beenregistered, a bit corresponding to the virtual volume in the k-th linegeneration management bitmap is set to “0”. On the other hand, whenthere is no updating registration in the k-th line block address of thevirtual volume, i.e., when “NONE” has been registered, a bitcorresponding to the virtual volume in the k-th line generationmanagement bitmap is set to “1”.

In the snapshot management table 2610 shown in FIG. 2A, bits of the1st-line generation management bitmap all become “0” as “0” is allocatedto the 1st-line block address No. 0 of each virtual volume. Bits of them-th line generation management bitmap all become 1 as “NONE” isallocated to the m-th line block address No. (m-1) of each virtualvolume.

In the snapshot management table 2610 shown in FIG. 2A, a size of theoriginal volume 310 is m blocks, and a maximum number of snapshots is n.For example, when a block size is 512 bytes, a size of the originalvolume 310 is 128 gigabytes, and a maximum number of snapshots is 64, asize m of the original volume is 250,000,000 blocks, and a maximumnumber n of snapshots is 64. A block size, a size of the original volume310, and a maximum number of snapshots may be optionally set because ofno influence on effects of this invention.

In the snapshot management table 2610 shown in FIG. 2A, in the 1st line(line 2616), the column 2611 indicates a block address No. 0 of theoriginal volume 310. The column 2612 indicates that the generationmanagement bitmap is 00 . . . 0. “0” of the columns 2613 to 2615indicates data of the block address No. 0 of virtual volumes 1, 2, . . .n corresponding to snapshots 1, 2, . . . n, i.e., that at the time ofissuing a snapshot creation request corresponding to each virtualvolume, data stored in the block address No. 0 of the original volume310 has been stored in the block address No. 0 of the snapshot volume330.

In the 2nd line (line 2617), the column 2611 indicates a block addressNo. 1 of the original volume 310. The column 2612 indicates that thegeneration management bitmap is 00 . . . 1. “1” of the column 2613indicates that data of a block address No. 1 of the virtual volume 1corresponding to the snapshot No. 1 have been stored in a block addressNo. 1 of the snapshot volume 330. “2” of the column 2614 indicates thatdata of a block address No. 1 of the virtual volume 2 corresponding tothe snapshot No. 2 have been stored in a block address No. 2 of thesnapshot volume 330. “NONE” of the column 2614 indicates that data of ablock address No. 1 of the virtual volume n corresponding to thesnapshot n have been stored in the block address No. 1 of the originalvolume 310.

Allocation of “NONE” to the block address No. 1 of the virtual volume nindicates that data of the block address No. 1 of the virtual volume nof the generation n have been stored in the block address No. 1 of theoriginal volume 310, and the data of the block address No. 1 of theoriginal volume 310 has not been updated after reception of an n-thsnapshot creation request corresponding to the virtual volume n.

In the 3rd line (line 2618), the column 2611 indicates a block addressNo. 2 of the original volume 310. The column 2612 indicates that thegeneration management bitmap is 11 . . . 1. The columns 2613, 2614, . .. 2615 indicate that data of a block address No. 2 of the virtualvolumes 1, 2, . . . n corresponding to the snapshots Nos. 1, 2, . . . nhave been stored in a block address No. 2 of the original volume 310(i.e., that the original volume 310 has not been updated).

In the m-th line (line 2619), the column 2611 indicates a block addressNo. (m-1) of the original volume 310. The column 2612 indicates that thegeneration management bitmap is 11 . . . 1. The columns 2613, 2614, . .. 2615 indicate that data of a block address No. (m-1) of the virtualvolumes 1, 2, . . . n corresponding to the snapshots Nos. 1, 2, . . . nhave been stored in a block address No. (m-1) of the original volume 310(i.e., that the original volume 310 has not been updated (rewritten)).

In other words, the generation management bitmap indicated in each entryof the column 2612 is a storage area which includes at least n bitsindicating a maximum number of snapshots, each bit corresponds to asnapshot number, and presence of updating after a start of maintaining asnapshot is indicated. In FIGS. 2A and 2B, “0” means updating while “1”means no updating.

The generation management bitmap 2612 is referred to when the snapshotmanagement program 241 writes block data in the original volume 310, andused to determine whether or not to copy data before updating of anaddress in which the data is written to the snapshot volume 330. Thegeneration management bitmap eliminates the necessity of referring toall the data in the snapshot management table 2610 to know a snapshot ofa virtual volume whose block address is rewritten for each data writing,whereby a data writing speed is increased.

FIG. 2B shows the snapshot block management table 2620.

The snapshot block management table 2620 shows correspondence between asnapshot volume block address 2621 and a generation assignment bitmap2622 to each block disposed in the snapshot volume 330 to manage a blockuse situation of the snapshot volume 330.

The generation assignment bitmap 2622 of each column is a storage areawhich includes at least n bits indicating a maximum number of snapshotcreations, and each bit corresponds to a number (generation number) of asnapshot. Each bit indicates whether a corresponding block on thesnapshot volume 330 is referred to or not (“1” means reference while “0”means no reference) as a block which constitutes a virtual volume toaccess corresponding snapshot data.

When block data of the original volume 301 is copied to the snapshotvolume 330 after writing executed in the original volume 310 based on arequest from the host 100, a bit in the generation assignment bitmap2622 corresponding to the snapshot number to refer to the block isupdated to 1. When a free block is obtained from the snapshot volume330, a block in which the bits of the generation assignment bitmap 2622are all 0 is selected.

When a snapshot is deleted, for all the blocks which constitute avirtual volume corresponding to the snapshot to be deleted, a bit in theassignment bitmap corresponding to the snapshot to be deleted is updatedto “0”.

Data of the snapshot block management table 2620 shown in FIG. 2B willbe described. A 1st line (2623) registers “11 . . . 1” as an assignmentbitmap of a block address No. 0 of the snapshot volume 330, whichindicates that a block of the block address No. 0 of the snapshot volume330 is used for all snapshots. As defined in the 1st line (2616) of thesnapshot management table 2610 shown in FIG. 2A, data of a block addressNo. 0 of virtual volumes 1, 2, . . . n corresponding to snapshots 1, 2,. . . n are stored in the block address 0 of the snapshot volume 330.

A 2nd line (2624) registers “10 . . . 0” as an assignment bitmap of ablock address No. 1 of the snapshot volume 330, which indicates that ablock of the block address No. 1 of the snapshot volume 330 is used fora snapshot No. 1 corresponding to a 1st bit of the assignment bitmap,i.e., constitutes a virtual volume 1, but it is not used for the othersnapshots. As defined in the 2nd line (2617) of the snapshot managementtable 2610 shown in FIG. 2A, data of a block address No. 1 of thevirtual volume 1 corresponding to the snapshot No. 1 are stored in theblock address No. 1 of the snapshot volume 330.

A 3rd line (2625) registers “01 . . . 0” as an assignment bitmap of ablock address No. 2 of the snapshot volume 330, which indicates that ablock of the block address No. 2 of the snapshot volume 330 is used fora snapshot No. 2 corresponding to a 2nd bit of the assignment bitmap,i.e., constitutes a virtual volume 2. As defined in the 3rd line (2618)of the snapshot management table 2610 shown in FIG. 2A, data of a blockaddress No. 1 of the virtual volume 2 corresponding to the snapshot No.2 are stored in the block address No. 2 of the snapshot volume 330.

Thereafter, setting is similar until a (p-1)-th line (2626).

That is, when at least one bit of the assignment bitmap 2622 is “1”, arelevant block of the snapshot volume 330 is used for a snapshot. Whenall the bits of the assignment bitmap 2622 are “0”, the block of thesnapshot volume 330 is not used for the snapshot. In other words, it isa free block.

Next, the process of the snapshot management program 241 will bedescribed.

FIG. 3 is a flowchart showing a writing process executed by the snapshotmanagement program 241.

The snapshot management program 241 first refers to the snapshotmanagement table 2610 to determine whether all the bits of thegeneration management bitmap 2612 corresponding to a block address of awriting process target are “0” or not (1001).

If all the bits are “0”, data of the block has been updated afterissuance of a last snapshot creation request, and virtual volumes haveall been correlated to the snapshot volume 330 for the block. Thus, whenall the bits of the generation management bitmap 2612 are “0”, it is notnecessary to copy data before updating to the snapshot volume 330. Then,proceeding to a step 1006, the data is written in a designated block ofthe original volume 310.

On the other hand, if at least one bit is “1”, there is a snapshot(virtual volume) which refers to the data of the original volume 310 tobe updated by the writing process, and thus the process proceeds to astep 1002.

In the step 1002, reference is made to the snapshot block managementtable 2620 shown in FIG. 2B to copy the data before updating stored inthe original volume 310 to be updated by the writing process to a freeblock of the snapshot volume 330.

Then, a value of the generation management bitmap referred to in thestep 1001 is stored in the generation assignment bitmap 2622 of thesnapshot block management table 2620 corresponding to an address of thefree block of the snapshot volume 330 set as a secondary side of thedata copying in the step 1002 (1003).

Subsequently, among the virtual volumes registered in the snapshotmanagement table 2610, a virtual volume corresponding to a bit having avalue “1” of the generation management bitmap referred to in the step1001 is specified. Then, the snapshot management table 2610 is updatedso that a block corresponding to a writing target block of the specifiedvirtual volume can correspond to the snapshot volume 330 set as thesecondary data copying side in the step 1002 (1004). In other words, theaddress of the block of the snapshot volume 330 set as the secondarydata copying side in the step 1002 is registered in a line correspondingto the writing target block address in a column corresponding to thespecified virtual volume of the snapshot management table 2610.

Next, values of all the bits of the generation management bitmapreferred to in the step 1001 are updated to “0” (1005).

Next, designated data is written in the block of the original volume 310indicated by the designated block address (1006). Then, the processcomes to an end.

FIG. 4 is a flowchart showing a reading process executed by the snapshotmanagement program 241.

The snapshot management program 241 first determines whether a readingtarget volume designated by the host 100 is the original volume 310 or avirtual volume of a snapshot. Based on a result of the determination,determination is made as to whether reading is from a snapshot or not(1101).

If a result shows that a read request received from the host 100corresponds to the original volume 310, the request is determined not tobe reading from the snapshot, and data is read from a designated blockaddress of the original volume 310 (1103).

On the other hand, if the read request received from the host 100 isfrom the virtual volume, the process proceeds to a step 1103 determiningthat the request is reading from the snapshot. Then, reference is madeto the snapshot management table 2610 shown in FIG. 2A to obtain a valuecorresponding to a block address of the reading target virtual volumedesignated by the host 100, and determination is made as to whether thevalue is “NONE” or not (1102).

If a result of the determination shows that the value corresponding tothe block address of the virtual volume is “NONE”, data of the readingtarget block of the virtual volume corresponding to the reading targetsnapshot has not been stored in the snapshot volume 330. Thus, data isread from the designated block address of the original volume 310(1103).

On the other hand, if the value of the block address referred to in thestep 1102 is not “NONE” but a given number, the block address of thereading target virtual volume is correlated to the block address in thesnapshot volume 330. In other words, data of the block address of thereading target virtual volume has been stored in the snapshot volume330. Thus, the data is read from the block address of the snapshotvolume 330 referred to in the step 1102 (1104).

Subsequently, the read block data is returned to the host 100 tocomplete the reading process.

FIG. 5 is a flowchart showing a snapshot creation process of thesnapshot management program 241.

Upon reception of a snapshot creation request from the host 100 or theCPU 220, the snapshot management program 241 registers virtual volumesof new generations in the snapshot management table 2610 shown in FIG.2A. Then, in the generation management bitmap 2612 registered in thesnapshot management table 2610, bits corresponding to the virtualvolumes newly registered corresponding to snapshots to be newly createdare all set to “1”. Block addresses of the virtual volumes correspondingto the snapshots to be newly created are all set to “NONE” (1201).

Next, data read from an area of the original volume 310 designated as atarget of snapshot creation is written in the snapshot volume 330. Then,the data stored in the designated area is copied from the originalvolume 310 to the snapshot volume 330 (1202).

Subsequently, the snapshot creation process comes to an end.

Incidentally, in the step 1201, in the generation management bitmap 2612registered in the snapshot management table 2610, values of all the bitscorresponding to the newly created virtual volumes are set to “1”.However, when there is an unused block in the original volume 310, ablock in the virtual volume corresponding to the unused block alsobecomes an unused block. At this time, a constitution may be employed inwhich in the unused block present in the newly created virtual volume,the bit corresponding to the newly created virtual volume is set to “1”in a block only other than the unused block of the generation managementbitmap. The unused block is a block not allocated for data (file,directory, or the like) storage, but prepared to store data when a fileor a directory is newly created or a size is increased thereafter.

Even when a write request in the unused block is issued, and data storedin the unused block is updated, no reference is made to the data of theunused block for the snapshot of the file system, and thus the dataupdating has no influence on the snapshot of the file system.Accordingly, when the unused portion is updated after snapshot creation,data before updating is not copied to the snapshot volume 330 if thegeneration management bitmap is “0” for the unused block during thesnapshot creation, and the data updating in the unused block isreflected on the snapshot, consequently causing a change in the data ofthe snapshot creation time. However, in the file system that uses thesnapshot, no influence is given on data of the file or the directorytherein. Thus, by setting the generation management bitmap to “0” forthe unused block when the snapshot is created, it is possible to reducethe amount of a generated difference.

Next, a creation process of the copy volume 320 will be described.

FIG. 6 is a flowchart showing a copy volume creation process of thesnapshot management program 241.

According to this embodiment, a full copy of the original volume 310 ofa given time is stored as a copy volume 320 in the storage.

First, the host 100 designates a generation to be set in the copy volume320, and sends a request of copying the original volume (2001). For thegeneration designation, for example, an optional generation (1stgeneration, 2nd generation, or the like) or a generation just before ageneration of a snapshot creation request can be designated.

Upon reception of the request, the snapshot management program 241copies all data of the original volume 310 of a present time to the copyvolume 320 (2002). Specifically, the original volume 310 and the copyvolume 320 are first synchronized with each other. Then, the blocks ofthe original volume 310 are all copied to the copy volume 320.Accordingly, a replication of the original volume 310 is created.

After completion of copying the original volume 310 to the copy volume320, the host 100 sends a snapshot creation request (2003). The snapshotmanagement program 241 that has received the snapshot creation requestfirst splits the original volume 310 from the copy volume 320 (2004).Thus, the original volume 310 and the copy volume 320 can both receiveaccess. The host 100 may instruct separation of the original volume 310from the copy volume 320.

Next, referring to the snapshot bitmap 261, information of a snapshotvolume of one generation is initialized (2005). Then, information of ageneration set in the copy volume 320 is set in the copy volumegeneration management information 262 (2006).

Next, determination is made as to whether a write request or a nextsnapshot creation request has been made from the host 100 or not (2007).

If there is a write request from the host, the process proceeds to astep 2008 to execute the writing process shown in FIG. 3. In otherwords, reference is made to the generation management bitmap 2612 of thesnapshot bitmap 261, and the data of the block has been updated if allthe bits are “0”. Then, data is written in the designated block of theoriginal volume 310.

On the other hand, if at least one bit is “1”, data of the block beforewriting is copied to the snapshot volume, and written in a designatedblock of the original volume 310.

In the step 2007, when a next snapshot creation request, i.e., asnapshot creation request designating a generation different from thatof the snapshot creation request made in the step 2003, comes from thehost 100, the process proceeds to a step 2009. When there are no suchrequests, the process stands by.

In the step 2009, determination is made as to whether a process end hasbeen instructed or not. If the process end has not been instructed, theprocess proceeds to a step 2010, and determines whether the generationdesignated by the snapshot creation request of the host 100 is differentor not from a generation set in the copy volume 320.

If the present generation of the copy volume 320 is similar to thedesignated generation, the process proceeds to a step 2014.

On the other hand, if the present generation of the copy volume 320 isdifferent from the designated generation, the process proceeds to a step2011, and determines whether any write requests have been made or notafter the previous snapshot creation request.

If no write request has been made, the process proceeds to the step2014. If a write request has been made, the process proceeds to a step2012, resynchronizes the original volume 310 with the copy volume 320,and copies all the data of the original volume 310 to the copy volume320. Upon completion of the copying, the original volume 310 is splitfrom the copy volume 320 (2013).

In the process from the step 2010 to the step 2013, for example, in thestep 2001, when a generation of the copy volume 320 is designated to beone generation before that of the snapshot creation request, a new writerequest made after the snapshot creation request causes the generationof the copy volume 320 to be two generations before. Thus,resynchronization is executed with the copy volume 320 to obtain a copyof the designated generation one before.

In the step 2014, information of a snapshot volume of one generation isinitialized from the snapshot bitmap 261. Then, information of the copyvolume 320 is registered in the copy volume generation managementinformation 262.

Through the process, the copy volume 320 of the designated generation iscreated.

FIG. 7 is a flowchart of a process of creating a designated generationvolume (virtual volume) by the generation volume create program 242.

The host 100 sends an access request a virtual volume of a designatedgeneration N. The generation volume create program 242 that has receivedthe access request determines whether the designated generation N issimilar to the current generation of the copy volume 320 or not (2201).As the information of the generation of the copy volume 320 has beenstored in the copy volume generation management information 262, thepresent copy volume generation can be obtained by referring to theinformation.

If the designated generation N is determined to be similar to that ofthe copy volume 320, data to which access has been requested are similarto those of the copy volume 320. Accordingly, the host 100 is instructedto access the copy volume 320 (2209), and the process is completed. Bythe process, the host 100 can access the virtual volume of thedesignated generation N.

If the designated generation N is determined to be different from thatof the copy volume 320, determination is first made as to whether thedesignated generation N is latest or not (2202). For the generationinformation of the copy volume 320, reference is made to the copy volumegeneration management information 262.

If the designated generation N is determined not to be latest, theprocess proceeds to a step 2208, a virtual volume of a designatedgeneration is designated from the copy volume 320 and the snapshotvolume 330, and the process is finished. Specifically, reference is madeto the snapshot bitmap 261 to obtain the virtual volume of thedesignated generation. In this case, block addresses of the originalvolume 310 and the copy volume 320 are similar to each other.Accordingly, for one of the blocks of the designated generation whichrefers to the original volume 310, reference to the block of the copyvolume 320 is instructed by using a block address of the block indicatedby the original volume block address 2611. Through the process, the host100 can access the virtual volume of the designated generation N.

In the step 2202, if the designated generation N is determined to belatest, after a request of a latest-generation snapshot is made,determination is made as to whether writing has been executed or not inthe original volume 310 (2203).

If the writing in the original volume 310 is determined to have beenexecuted, the original volume 310 is resynchronized with the copy volume320 to create data of the latter similar to those of the former (2204).Then, the original volume 310 is split from the copy volume 320 (2205).At a point of this time, the data of the copy volume 320 is similar tothose of the original volume 310, i.e., in a latest state. Next,information of the copy volume 320 is registered in the copy volumegeneration management information 262 (2206). Then, access to the copyvolume 320 is instructed (2207) to finish the process. Through theprocess, the host 100 can access the virtual volume of the designatedgeneration N.

If no writing is determined in the step 2203, data to which access hasbeen requested is similar to those of the copy volume 320. Thus, thehost 100 is instructed to access the copy volume 320 (2207) to finishthe process. Through the process, the host 100 can access the virtualvolume of the designated generation N.

FIG. 8 is a flowchart showing a process of creating a designatedgeneration volume (virtual volume) by the generation volume createprogram 242. According to the process, when interference occurs in thecopy volume 320 or the like, data of the copy volume 320 is created in anew drive (logical volume) to restore the copy volume 320.

The host 100 detects the occurrence of interference or the like in thecopy volume 320, and sends a request of creating a generation N of thecopy volume 320 as a new volume. The generation volume create program242 that has received the request first determines whether thedesignated generation N is a latest generation or not (2401). If thedesignated generation N is determined to be latest, since data of theoriginal volume 310 is similar to those of the copy volume 320, the dataof the original volume 310 is copied to the restoration target logicalvolume. At this time, using information of the logical volume asinformation of the copy volume 320, mapping information of the snapshotbitmap 261, the copy volume generation management information 262 or thelike is changed to finish the process (2402).

On the other hand, if the designated generation N is determined not tobe latest, a volume of a generation before a time of a last snapshotcreation request is created in a new logical volume from the originalvolume 310 and the snapshot volume 330 (2403). Specifically, a virtualvolume of a generation of the time of the last snapshot creation requestis copied to a new logical volume from the present original and snapshotvolumes 310 and 330.

Next, a virtual volume of a designated generation is created based ondata of the logical volumes, i.e., data of the original and snapshotvolumes 310 and 330 of the generation of the time of the last snapshot,and copied to the restoration target logical volume of the copy volume320 (2404).

Specifically, the virtual volume of the designated generation isobtained by referring to the snapshot bitmap 261. In this case, blockaddresses of the data of the logical volume of the generation of thetime of the last snapshot and the original volume 310 are similar toeach other. Thus, for one of the designated generation blocks whichrefers to the original volume 310, reference is made to a block of thelogical volume by using a block address of the block indicated by anoriginal volume block address 2611.

Through the process, since the virtual volume of the designatedgeneration can be obtained, the virtual volume is copied to therestoration target logical volume of the copy volume 320.

By the virtual volume creation process, when interference occurs in thecopy volume, it is possible to restore the copy volume to a new logicalvolume from the original volume 310 and the snapshot volume 330.

FIG. 9 is a flowchart showing a process of restoring the original volume310 by the original volume restore program 243.

Due to interference or the like in the original volume 310, the host 100sends a request of creating the original volume 310 as a new volume of adesignated generation N. The original volume restore program 243 thathas received the request first determines whether the designatedgeneration N is a generation of the copy volume 320 or not (2601). Ifthe designated generation N is similar to that of the copy volume 320,data of the copy volume 320 can be directly used as those of theoriginal volume 310. Accordingly, the copy volume 320 is changed toinformation of the original volume 310, and mapping information of thesnapshot bitmap 261, the copy volume generation management information262 or the like is changed to finish the process (2606).

On the other hand, if the generation of the copy volume 320 is differentfrom the designated generation N, first, referring to the snapshotbitmap 261, for a block address of the designated generation indicatingthe snapshot volume 330, data of the block address is overwritten in thecopy volume 320 (2602).

Next, a generation number of the present original volume 310 is stored(2603).

Next, data of generations (N+1 generation and afterward) newer than thedesignated generation N of the copy volume 320 and the snapshot volume330 are discarded. Further, data of the snapshot bitmap 261 is discarded(2604).

Next, the information of the snapshot bitmap 261 is updated to a blockaddress of the present copy volume 320. The block addresses of theoriginal volume 310 and the copy volume 320 are similar, with the resultthat the address becomes a block address of a new restored originalvolume (2605).

Then, mapping information of the copy volume 320 is changed toinformation of the original volume 310. Specifically, the copy volume320 is changed to the original volume 310 by changing the mappinginformation of the snapshot bitmap 261, the copy volume generationmanagement information 262 or the like. Then, the process is finished(2606).

By the above process, when interference occurs in the original volume310, it is possible to restore the original volume 310 to a new logicalvolume from the copy volume 330 and the snapshot volume 330.

FIG. 10 is a flowchart showing a process of creating a designatedgeneration volume (virtual volume) by the generation volume createprogram 242. According to the process, when interference occurs in thesnapshot volume 330 or the like, access is made to the virtual volume ofthe designated generation without using any snapshot volumes.

The host 100 sends an access request a virtual volume of a designatedgeneration N. The generation volume create program 242 that has receivedthe request determines whether the designated generation N is a latestgeneration or not (2701). It should be noted that generation informationof the copy volume 320 is obtained by referring to the copy volumegeneration management information 262.

In the step 2701, if the designated generation N is determined to belatest, after a request of a latest-generation snapshot is made,determination is made as to whether writing has been executed or not inthe original volume 310 (2702).

If the writing in the original volume 310 is determined to have beenexecuted, the original volume 310 is resynchronized with the copy volume320 to create data of the latter similar to those of the former (2703).Then, the original volume 310 is split from the copy volume 320 (2704).At a point of this time, the data of the copy volume 320 are similar tothose of the original volume 310, i.e., in a latest state.

Next, information of the copy volume 320 is registered in the copyvolume generation management information 262 (2705). Then, access to thecopy volume 320 is instructed (2706) to finish the process. Through theprocess, the host 100 can access the virtual volume of the designatedgeneration N.

If no writing is determined in the step 2702, data to which access hasbeen requested is similar to those of the copy volume 320. Thus, thehost 100 is instructed to access the copy volume 320 (2703) to finishthe process. Through the process, the host 100 can access the virtualvolume of the designated generation N.

If the designated generation N is determined not to be latest in thestep 2701, the process proceeds to a step 2707, and determines whetherthe designated generation N is similar to that of the present copyvolume 320 or not.

If the designated generation N is similar to that of the present copyvolume 320, information of the copy volume 320 is registered in the copyvolume generation management information 262 (2705).

Next, access to the copy volume 320 is instructed (2706) to finish theprocess. Through the process, the host 100 can access the virtual volumeof the designated generation N.

On the other hand, if the designated generation N is determined not tobe similar to that of the present copy volume 320 in the step 2707, thegeneration N is present in a block address stored in the snapshot volume330. However, writing in the snapshot volume 330 is impossible due tointerference. Thus, the generation volume create program 242 transmits amessage that a virtual volume of the generation N cannot be created tothe host 100 which makes access (2708), and finishes the process.

FIG. 11 is a flowchart showing a capacity management process of thesnapshot volume 330 by the snapshot volume capacity management program244.

The snapshot volume capacity management program 244 is started when awrite request (updating) in the snapshot volume 330 is received. Theprogram 244 monitors a total use amount of the snapshot volume 330 so asnot to exceed a predetermined threshold. If exceeded, a process such asbackup in the tape library 400 is carried out.

The snapshot volume capacity management program 244 first determineswhether writing has been executed or not in the snapshot volume 330(2901). If no writing has been executed, the process stands by untilwriting is executed.

If writing is determined to have been executed, determination is made asto whether a total use amount of the snapshot volume 330 becomes equalto or higher than the predetermined threshold or not (2902). The useamount of the snapshot volume 330 has been stored in the capacitymanagement information 264 registered at a time of accessing thesnapshot volume 330. If the total use amount of the snapshot volume isless than the predetermined threshold, the process returns to the step2901. If the total use amount of the snapshot volume is equal to orhigher than the predetermined threshold, a generation of low priority(generation M) is searched for in the data of the snapshot volume 330.

For priority determination, a generation that includes data that has notbeen accessed for a predetermined time from last access, a generationthat includes data of low access frequency, and a generation of a largevolume of the data are judged to be low in priority.

Next, a volume of the searched generation M of low priority is created(2904). In this case, access may be accepted as a virtual volume, or thevolume may be copied to a new logical volume. Then, the volume of thegeneration M is backed up in the tape library 400 (2905).

Next, information of the generation M is deleted (2906). Specifically,data which the generation M only refers to is specified by referring tothe snapshot block management table 2620. Then, the specified data whichthe generation M only refers to is deleted from the snapshot volume 330.Subsequently, the information of the generation M is deleted from thesnapshot bitmap 261.

Through the process, the use amount of the snapshot volume 330 can beset to a volume which does not exceed the predetermined threshold.

A capacity of the snapshot volume 330 can be dynamically managed byuser's designation. For example, when the user designates the number ofgenerations, if the capacity of the snapshot volume 330 reaches an upperlimit at the number of generations smaller than the designated number ofgenerations, data of the old generations are backed up in the tapelibrary 400. When the user designates a capacity of the snapshot volume330, the data of the old generations are backed up in the tape library400 until the designated capacity can be secured. In place of the backupin the tape library 400, the data of the generations may be deleted. Theuser may instruct backup in the tape library 400. The user may instructdeletion of the data of the generations.

Next, an operation example to which the storage system is applied willbe described.

FIG. 12 shows an example of restoring data of the original volume 310 tothose before a time of illegal writing when the past illegal writing isdetected in the storage control unit 200.

When the user discovers illegal writing, the following process iscarried out.

First, the user refers to the snapshot information 263 in the commonmemory of the storage control unit 200 from the host 100. In thesnapshot information 263, a time and a generation number of a snapshotare stored. Thus, the user obtains a generation number (generation L)registered at a time before the time of illegal writing (3001).

Next, the user sends a request of returning the original volume 310 tothe generation L to the storage control unit 200 (3002).

In the storage control unit 200 that has received the request, theoriginal volume restore program 243 restores the original volume of thedesignated generation L. Specifically, first, virtual volumes of thegeneration L are obtained by referring to the snapshot bitmap 261. For avirtual volume among those of the generation L which indicates a blockaddress of the snapshot volume 330, a block address thereof is copied tothe original volume 310. Accordingly, the original volume 310 of thedesignated generation L is created (3003).

After the original volume 310 has become the generation L, informationof generations newer than the generation L is deleted (3004).

Then, the original volume 10 is resynchronized with the copy volume 320to create data of the latter similar to those of the former (3005).Subsequently, the original volume 310 is split from the copy volume 320(3006). Thus, the data of the copy volume 320 become similar to those ofthe original volume 310.

Through the process, the original volume 310 can be restored to a pastoptional generation by user's designation. It should be noted that, inplace of restoring the original volume 310 to the designated generation,the copy volume 320 may be set to the designated generation L, and thenmapping information may be changed to change the copy volume of thegeneration L to the original volume 310.

FIG. 13 shows another operation example to which the storage system isapplied.

The user sends a time of illegal writing and a restore request of theoriginal volume to the storage control unit 200 from the host 100. Uponreception of the request, the storage control unit 200 automaticallyrestores data of the original volume 310 to those before the time of theillegal writing.

When the user discovers illegal writing, the following process iscarried out.

First, the user sends a time of illegal writing and a restore request ofthe original volume to that of a generation immediately before the time(3101).

In the storage control unit 200 that has received the request, theoriginal volume restore program 243 obtains the designated time, andsearches for a generation immediately before the time (3102).Specifically, a generation K is searched, which satisfies the followingformula in which “T3” is a designated time and TK is a time ofsnapshooting the generation K:TK<T3<TK+1

By the formula, the generation K is obtained in which the time ofsnapshooting the generation K is before the designated time T3, and atime of snapshooting a generation K+1 as a generation subsequent to thegeneration K is after the designated time T3. Alternatively, ageneration K that satisfies the following formula is searched for:TK=T3

By the formula, the generation K is obtained in which the time ofsnapshooting the generation K is similar to the designated time T3.

Thus, the generation K immediately before the designated time T3 isobtained.

Next, the original volume 310 is restored to the obtained generation K.

Specifically, virtual volumes of the generation K are obtained byreferring to the snapshot bitmap 261. For one of the virtual volumes ofthe generation K which indicates a block address of the snapshot volume330, the block address is copied to the copy volume 310. Accordingly,the original volume 310 of the designated generation K is created(3103).

After the original volume 310 becomes the generation K, information ofgenerations newer than the generation K is deleted (3104).

Then, the original volume 310 is resynchronized with the copy volume 320to create data of the latter similar to those of the former (3105).Subsequently, the original volume 310 is split from the copy volume 320(3106). Accordingly, the data of the copy volume become similar to thoseof the original volume 310.

Through the process, by user's time designation, the original volume 310can be restored to a past optional generation. It should be noted that,in place of restoring the original volume 310 to the designatedgeneration, the copy volume 320 may be set to the designated generationK, and then mapping information may be changed to change the copy volumeof the generation K to the original volume 310.

As described above, according to the storage system of the firstembodiment of this invention, since the storage 300 includes theoriginal volume 310, the copy volume 320 for storing the full copy ofthe original volume 310 at a given time, and the snapshot volume 330 forstoring the snapshot of the data written in the original volume 310, thevolume of the designated generation can be obtained. Thus, it ispossible to store the backup of the designated generation in the storagesystem, and to access and back up the data of the designated generationwithout using a tape library or other such devices of a lowcommunication speed while a storage capacity is kept low.

Next, a second embodiment of this invention will be described.

According to the second embodiment of this invention, a copy volume 320backs up data in real time at a time of access to an original volume inplace of obtaining a copy of data of a designated generation. Componentssimilar to those of the first embodiment are denoted by similarreference numerals, and description thereof will be omitted.

FIG. 14 is a flowchart showing a copy volume creation process of asnapshot management program 241 according to the second embodiment ofthis invention. FIG. 14 is similar to FIG. 6, but data of the copyvolume 320 is always updated when a write request comes from a host 100.

Upon start of the process, the snapshot management program 241 copiesall data of the original volume 310 of a present time to the copy volume320 (2101). Specifically, the original volume 310 and the copy volume320 are synchronized with each other. Then, blocks of the originalvolume 310 are all copied to the copy volume 320. Accordingly, a copy ofthe original volume 310 is created.

After completion of copying the original volume 310 to the copy volume320, the host 100 sends a snapshot creation request (2102). The snapshotmanagement program 241 that has received the snapshot creation requestfirst splits the original volume from the copy volume. Then, referringto a snapshot bitmap 261, information of a snapshot volume of onegeneration is initialized (2103).

Next, determination is made as to whether a write request or a nextsnapshot creation request has been made from the host 100 or not (2104).

If there is a write request from the host, the process proceeds to astep 2105 to execute writing shown in FIG. 3. In other words, referenceis made to a generation management bitmap 2612 of the snapshot bitmap261, and the data of the block has been updated if all the bits are “0”.Then, data is written in the designated block of the original volume310.

On the other hand, if at least one bit is “1”, data of the block beforewriting is copied to the snapshot volume, and written in a designatedblock of the original volume 310.

Upon completion of the writing process, data (updated block) written inthe original volume 310 is also written in the copy volume 310 (2106).

In the step 2104, when a next snapshot creation request comes from thehost 100, i.e., a snapshot creation request designating a generationdifferent from that of the snapshot creation request made in the step2102, the process proceeds to a step 2107. When there are no suchrequests, the process is repeated and waits for a request.

In the step 2107, whether or not to finish the process is determined. Ifthe process is not finished, the process returns to the step 2104, andprepares for a write request from the host 100.

Through the process, when the write request in the block of the originalvolume 310 comes from the host 100, writing is executed in a similarblock of the copy volume 320, and a copy similar to the state of theoriginal volume 310 is always stored.

FIG. 15 is a flowchart showing a process of creating a designatedgeneration volume (virtual volume) by a generation volume create program242 according to the second embodiment of this invention. FIG. 15 issimilar to FIG. 7, but the copy volume 320 always holds a copy of dataof the original volume 310.

The host 100 sends an access request a virtual volume of a designatedgeneration N. The generation volume create program 242 that has receivedthe request splits the original volume 310 from the copy volume 320(2301).

Next, generation information of the present copy volume 320 isregistered in a copy volume generation management information 262(2302). Then, data of the snapshot bitmap 261 is updated.

Next, determination is made as to whether the generation N designatedfrom the host 100 is latest or not (2302). If the designated generationN is determined to be latest, data to which access has been requested issimilar to those of the copy volume 320. Accordingly, the host 100 isinstructed to access the copy volume 320 (2304) to finish the process.Through the process, the host 100 can access a virtual volume of thedesignated generation N.

On the other hand, if the designated generation N is determined not tobe latest, the process proceeds to a step 2208, a virtual volume of adesignated generation is designated from the copy volume 320 and thesnapshot volume 330, and the process is finished (2305). Specifically,reference is made to the snapshot bitmap 261 to obtain the virtualvolume of the designated generation. In this case, block addresses ofthe original volume 310 and the copy volume 320 are similar to eachother. Accordingly, for one of the blocks of the designated generationwhich refers to the original volume 310, reference is made to the blockof the copy volume 320 by using a block address of the block indicatedby an original volume block address 2611. Through the process, the host100 can access the virtual volume of the designated generation N.

By the process, even in a constitution in which the data of the originalvolume 310 and the copy volume 320 are always synchronized with eachother, access can be made from the host to the designated generationvolume.

FIG. 16 is a flowchart showing a process of creating a designatedgeneration volume (virtual volume) by a generation volume create program242 according to the second embodiment of this invention. According tothe process, when interference occurs in the copy volume 320 or thelike, data of the copy volume 320 is created in a new drive (logicalvolume) to restore the copy volume 320. FIG. 16 is similar to FIG. 8,but the copy volume 320 always holds a copy of data of the originalvolume 310.

The host 100 detects the occurrence of interference or the like in thecopy volume 320, and sends a request of creating a generation N of thecopy volume 320 as a new volume. The generation volume create program242 that has received the request first determines whether thedesignated generation N is a latest generation or not (2501). If thedesignated generation N is determined to be latest, since data of theoriginal volume 310 is similar to those of the copy volume 320, the dataof the original volume 310 is copied to the restoration target logicalvolume.

At this time, using information of the logical volume as information ofthe copy volume 320, mapping information of the snapshot bitmap 261, thecopy volume generation management information 262 or the like is changedto finish the process (2502).

On the other hand, if the designated generation N is determined not tobe latest, a volume of the designated generation N is created in a newlogical volume from the original volume 310 and the snapshot volume 330(2503).

In other words, a virtual volume of the designated generation is createdfrom data of the original volume 310 and data of the snapshot volume330, and copied to a restoration target logical volume of the copyvolume 320. Specifically, the virtual volume of the designatedgeneration is obtained by referring to the snapshot bitmap 261.

Through the process, since the virtual volume of the designatedgeneration can be obtained, the virtual volume is copied to therestoration target logical volume of the copy volume 320.

By the volume creation process, when interference occurs in the copyvolume, it is possible to restore the copy volume to a new logicalvolume from the original volume 310 and the snapshot volume 330.

FIG. 17 is a flowchart showing a process of creating a designatedgeneration volume (virtual volume) by the generation volume createprogram 242 according to the second embodiment of this invention.According to the process, when interference occurs in the snapshotvolume 330 or the like, access is made to the virtual volume of thedesignated generation without using any snapshot volumes. FIG. 17 issimilar to FIG. 10, but the copy volume 320 always holds a copy of dataof the original volume 310.

The host 100 sends an access request a virtual volume of a designatedgeneration N. The generation volume create program 242 that has receivedthe request determines whether the designated generation N is a latestgeneration or not (2801). It should be noted that generation informationof the copy volume 320 is obtained by referring to the copy volumegeneration management information 262.

In the step 2801, if the designated generation N is determined to belatest, information of the copy volume 320 is registered in the copyvolume generation management information 262 (2802). Next, access to thecopy volume is instructed (2803) to finish the process. Through theprocess, the host 100 can access the virtual volume of the designatedgeneration N.

In the step 2801, if the designated generation N is determined not to belatest, the generation N is present in a block address stored in thesnapshot volume 330. However, reading in the snapshot volume 330 isimpossible due to interference. Thus, the generation volume createprogram 242 sends a message that the generation N cannot be accessed tothe host 100 which makes access (2804) to finish the process.

As described above, according to the storage system of the secondembodiment of this invention, since the storage 300 includes theoriginal volume 310, the copy volume 320 for always storing the fullcopy of the original volume 310, and the snapshot volume 330 for storingthe snapshot of the data written in the original volume 310, the volumeof the designated generation can be obtained as in the first embodiment.Thus, it is possible to store the backup of the designated generation inthe storage system, and to access and back up the data of the designatedgeneration without using a tape library of a slow communication speedwhile a storage capacity is kept low. Especially, since a data backup ofthe original volume is provided in real time, data is quickly restoredeven when interference occurs in the disk devices.

While the present invention has been described in detail and pictoriallyin the accompanying drawings, the present invention is not limited tosuch detail but covers various obvious modifications and equivalentarrangements, which fall within the purview of the appended claims.

1. A storage system comprising: a disk device which includes: anoriginal volume for storing data which is read/written by a host; and asnapshot volume for storing snapshot data of a plurality of snapshotgenerations of the original volume; and a storage control unit whichincludes: a processor unit; a memory storing information of each of theplurality of snapshot generations; a channel I/F that is coupled to thehost; and a device I/F that is coupled to the disk device; and a tapedevice coupled to the storage control unit; wherein when the processorunit receives write data to a storage area of the original volume, theprocessor determines whether data stored in the storage area of theoriginal volume is already copied to the snapshot volume or not; if thedata stored in the storage area of original volume is not already copiedto snapshot volume, the processor unit copies the data from originalvolume to the snapshot volume; when a use capacity of the snapshotvolume is larger than a threshold amount, the processor unit indicates aspecified snapshot generation; the processor unit migrates data of thespecified snapshot generation from the snapshot volume to tape device;and the processor unit deletes information of the specified snapshotgeneration in the snapshot volume.
 2. The storage system according toclaim 1, wherein: the specified snapshot generation specified by theprocessor unit is a snapshot generation including data that has not beenaccessed for a predetermined time.
 3. The storage system according toclaim 1, wherein: the specified snapshot generation specified by theprocessor unit is a snapshot generation including data of low accessfrequency.
 4. The storage system according to claim 1, wherein: thespecified snapshot generation specified by the processor unit is asnapshot generation whose data amount is large.
 5. The storage systemaccording to claim 1, wherein: the threshold amount is designated by auser.
 6. A storage system comprising: a disk device which includes: anoriginal volume for storing data which is read/written by a host; and asnapshot volume for storing snapshot data of a plurality of snapshotgenerations of the original volume; and a storage control unit whichincludes: a processor unit; a memory storing information of each of theplurality of snapshot generations; a channel I/F that is coupled to thehost; and a device I/F that is coupled to the disk device; wherein whenthe processor unit receives write data to a storage area of the originalvolume, the processor determines whether data stored in the storage areaof the original volume is already copied to the snapshot volume or not;if the data stored in the storage area of original volume is not alreadycopied to snapshot volume, the processor unit copies the data from theoriginal volume to the snapshot volume; when a use capacity of thesnapshot volume is larger than a threshold amount, the processor unitindicates a specified snapshot generation; and the processor unitdeletes data of the specified snapshot generation from the snapshotvolume.
 7. The storage system according to claim 6, wherein: thespecified snapshot generation specified by the processor unit is asnapshot generation including data that has not been accessed for apredetermined time.
 8. The storage system according to claim 6, wherein:the specified snapshot generation specified by the processor unit is asnapshot generation including data of low access frequency.
 9. Thestorage system according to claim 6, wherein: the certain snapshotgeneration specified by the processor unit is a snapshot generationwhose data amount is large.
 10. The storage system according to claim 6,wherein: the threshold amount is designated by a user.